The present invention relates to a recording/reproducing apparatus using tape, e.g. VTR, particularly to a tape travel controlling system and tape guide construction both suitable for stabilizing the traveling of tape.
The following two points are mentioned as factors of impeding a stable traveling of tape.
1) Variation in width of tape used.
2) Variation in winding height in the tape width direction, so-called "stepped winding," at a tape winding reel portion.
In connection with the above points 1) and 2), the following description is now provided about the respective present situations.
First, as to the above point 1), in today's tape recorders, for example in video tape recorders, a high density recording is the trend of the world. To this end, also as to the recording format, there is a tendency to narrower tracks. In order to ensure interchangeability under this situation, the accuracy of the width of tape as a recording medium is an important point.
More particularly, for ensuring interchangeability in a video tape recorder, a track pattern must be formed on tape so as to conform to a standardized recording format with a high accuracy. To this end, it is first required to suppress changes in the width direction of tape which is traveling. For this purpose, tape guides which define a tape traveling path in a video tape recorder are provided with flange portions for contact with the upper and lower ends of tape, thereby suppressing changes in the tape width direction. However, if the tape width accuracy is low and there is a width variation (variation from an average width value) or a width deviation (difference between average width values), an actual tape traveling path will be different from a tape traveling path which can form a track pattern conforming to the format defined by the flange portions of the tape guides. As a result, the linearity of a recording track formed on the tape is deteriorated and so at the time of playback in another video tape recorder there occurs a tracking error, leading to deterioration of reproducing characteristics.
A method commonly adopted for suppressing such deterioration in linearity of the recording track is to enhance the accuracy of the tape width. For example, according to a standard established in March 1982 regarding VHS type video tape recorders, the accuracy of the tape width is specified to be .+-.10 .mu.m, and the linearity of the recording track is thereby defined to be 10 .mu.m.sub.p-p. According to the recent tape processing technique, there is attained a tape width accuracy of about 4 to 6 .mu.m.sub.p-p, thus fully satisfying the above condition, and the amount of deterioration in linearity of the recording track is about 2 to 3 .mu.m.sub.p-p, thus causing no specially serious problem in connection with the above condition.
However, according to a standard established on small-sized cassette high-definition VTR systems established in June 1989, the accuracy of the recording track linearity is specified to be 4 .mu.m.sub.p-p. In this case, the deterioration of the recording track linearity based on the foregoing tape width accuracy of 2 to 3 .mu.m.sub.p-p becomes a serious problem.
One method for solving this problem is to further improve the tape width accuracy. However, since the tape is thin and long and such further improvement leads to an increase of cost, it is very difficult to further improve the tape width accuracy. In this connection, there has been found no example of any measure taken for the tape recorder body.
Now, the following description is provided about the present situation of the foregoing point 2). In a tape recorder, a tape is wound round two reels, and for example in the case of a cassette tape for 8 mm VTR, such reels are each provided with a pair of flange portions in corresponding relation to both edges of the tape. In a compact cassette for audio or DAT, though such flanges are not formed, two sheets are provided in the cassette to sandwich a tape in the tape width direction.
Such flanges or sheets are for preventing the tape from coming off a reel when wound round the reel or for preventing the tape from being displaced in its width direction and resulting in the so-called "stepped winding." There will be no such stepped winding if the spacing between the paired flanges or the two sheets is in conformity with the tape width. On the other hand, if a tape edge comes into sliding contact with such flange or sheet, there will occur a change in the tape traveling speed or damage of the tape edge. Therefore, it has heretofore been required to set the spacing between the paired flanges or two sheets somewhat larger than the tape width although the said spacing is set as close as possible to the tape width. For example, according to the standard on 8 mm VTR, the reel flange spacing is specified to be 8.3 to 8.9 mm relative to the tape width of 8.0 mm.
In the above prior art, therefore, the formation of a stepped winding corresponding to the larger spacing set as above has been unavoidable. But if there is a stepped winding on the tape wound-up reel, when the tape is then delivered from the reel, the tape traveling height varies in the reel position by an amount corresponding to the difference in height of the stepped winding, thus giving rise to the problem that the track tracing performance at the time of recording or reproducing is deteriorated.
Besides, a tape edge comes into strong sliding contact with a flange portion of a tape guide disposed near the reel. Further, the tape will undergo an out-of-plane deformation, so-called buckling, near the sliding contact portion with the flange, thus causing damage of the tape.
As an example of a measure taken against such problem, reference is here made to Japanese Patent Laid Open Nos. 1-224966 and 1-269268. In these two publications, a tape traveling height is detected by a sensor disposed near the supply reel and a control is made by feeding back the amount of variation in the said height to move the reel vertically. According to the disclosures of the publications in question, the traveling height of the tape delivered from the supply reel is thereby maintained constant and so the abovementioned problem is overcome.